FIGS. 25 and 26 show one example of a conventional sealing structure in a rotating wheel mechanism of this type of construction machines. FIG. 25 shows the upper part of the sealing structure, and FIG. 26 shows the lower part thereof. In the rotating wheel mechanism, a floating seal 101 composed of a ring at the fixed side and a ring at the rotating side, which are fitted to each other, is provided in order to prevent lubricant oil for a bearing 100 from leaking, and to prevent dirt and dust from entering. Also, a fixed seal member 103 is secured to the vehicle body 102 on the outer circumference of the floating seal 101, and a rotating seal member 105 is provided at the rotating wheel 104. An inner circumferential gap seal 106 and an outer circumferential gap seal 107 are provided between these seal members 103 and 105. Further, a space 108 positioned between the inner circumferential gap seal 106 and the outer circumferential gap seal 107 is formed between the seal members 103 and 105. As shown in FIG. 26, at the outer circumferential gap seal 107 and the space 108, the lower part of a circumferential area about the center of rotation of the rotating wheel 104 is opened downward.
The outer circumference of the floating seal 101 is sealed by the gap seals 106 and 107, dirt is prevented from entering from above the position of the floating seal 101. In addition, dirt that has entered the portion of the floating seal 101 drops and is discharged from the opening at the lower part of the space 108.
However, as shown by double dotted chain lines in FIGS. 25 and 26, dirt D is apt to be adhered to and accumulated on the vehicle body 102 and the rotating wheel 104 in a state where dirt D encloses the seal members 103 and 105. In particular, if soil at a work site is, for example, clay, a great deal of dirt D is apt to be thickly accumulated. Therefore, there is a large possibility that a great deal of the accumulated dirt D will enter the portion of the floating seal 101 through the gap seals 106 and 107. For this reason, there is a problem that the sealing property of the floating seal 101 is lost at an early stage, and the service life of the seal is reduced. In particular, where accumulated substances like clay are dried and solidified, the accumulated substances turn granular or powdery to easily pass through the gap seals 106 and 107 and always drop. This can become a cause for further shortening of the service life of the floating seal 101.
In addition, dropping of dirt from the space 108, etc., is hindered by the accumulated dirt at the lower part of the seal members 103 and 105, and further adverse influences are given to the service life of the floating seal 101.
On the other hand, as the rotating wheel mechanism aiming at the sealing property of the outside seal of the floating seal in this type of construction machines, for example, the rotating wheel mechanisms constructed as disclosed by Patent Documents 1 and 2 have been proposed. That is, in the construction described in Patent Document 1, a notched portion to vary the gap amount is formed on the wall at the rotating wheel, which composes the outside seal consisting of a gap. The pressure of entering dirt is changed by varying the gap amount at the notched portion, wherein the amount of the dirt from the outside can be reduced. Further, in the construction described in Patent Document 2, an annular inclination portion that is gradually enlarged so as to have a large diameter toward the housing is formed on the wall at the rotating wheel, which wall composes the outside seal consisting of a gap. When the rotating wheel rotates, dirt that has entered the interior are discharged outside via the inclination portion of the gap by a centrifugal force.
However, in the prior art constructions according to Patent Documents 1 and 2, no countermeasures are taken against dirt accumulated on the outer circumference of the outside seal. Therefore, it is difficult to remove adverse influences against the floating seal due to the accumulated dirt described above.
Patent Document 1: Japanese Laid-Open Utility Model Publication No. 5-90051
Patent Document 2: Japanese Laid-Open Patent Publication No. 2000-346205